The broad objective is to determine the way in which genes cooperate to bring about the orderly growth and development of an organism. The proposed work would seek to determine to what extent the genetic mechanisms which control developmental pathways in a higher organism are similar to the genetic mechanisms which control biosynthetic pathways in a microorganism, and to what extent higher organisms may have evolved new kinds of genetic control mechanisms. The objectives would include identifying and characterizing as many as possible of the genes involved in controlling alternative pathways of development of certain body segments of Drosophila. Already a tightly linked "bithirax" cluster of at least seven genetic units located in the right arm of the third chromosome has been characterized. These units are dependent upon proximity for their normal functioning, and as a result the bithorax cluster somewhat resembles in properties the operonic type of gene cluster which Jacob and Monod discovered in bacteria. The proposed research may help to provide an understanding of the basis for human congenital malformations since the underlying genetic and biochemical mechanisms which control developmental pathways in animals may be very similar to those which control developmental pathways in human beings.